Apparatus and method for treating tumors near the surface of an organ

ABSTRACT

A system for treating a target region in tissue beneath a tissue surface comprises a probe for deploying an electrode array within the tissue and a surface electrode for engaging the tissue surface above the treatment site. Preferably, surface electrode includes a plurality of tissue-penetrating elements which advance into the tissue, and the surface electrode is removably attachable to the probe. The tissue may be treated in a monopolar fashion where the electrode array and surface electrode are attached to a common pole on an electrode surgical power supply and powered simultaneously or successively, or in a bipolar fashion where the electrode array and surface electrode are attached to opposite poles of the power supply. The systems are particularly useful for treating tumors and other tissue treatment regions which lie near the surface.

This application is a continuation-in-part of application Ser. No.09/124,152, filed on Jul. 28, 1998, the full disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the structure and use ofradiofrequency electrosurgical apparatus for the treatment of solidtissue. More particularly, the present invention relates to anelectrosurgical system having pairs of electrodes and electrode arrayswhich are deployed to treat large volumes of tissue, particularly forthe treatment of tumors which lie close to the surface of an organ.

The delivery of radiofrequency energy to target regions within solidtissue is known for a variety of purposes. Of particular interest to thepresent invention, radiofrequency energy may be delivered to diseasedregions in target tissue for the purpose of causing tissue necrosis. Forexample, the liver is a common depository for metastases of many primarycancers, such as cancers of the stomach, bowel, pancreas, kidney, andlung. Electrosurgical probes for deploying multiple electrodes have beendesigned for the treatment and necrosis of tumors in the liver and othersolid tissues. See, for example, the LeVeen™ Needle Electrode availablefrom RadioTherapeutics Corporation which is constructed generally inaccord with published PCT application WO 96/29946.

The probes described in WO 96/29946 comprise a number of independentwire electrodes which are extended into tissue from the distal end of acannula. The wire electrodes may then be energized in a monopolar orbipolar fashion to heat and necrose tissue within a defined volumetricregion of target tissue. In order to assure that the target tissue isadequately treated and to limit damage to adjacent healthy tissues, itis desirable that the array formed by the wire electrodes within thetissue be precisely and uniformly defined. In particular, it isdesirable that the independent wire electrodes be evenly andsymmetrically spaced-apart so that heat is generated uniformly withinthe desired target tissue volume. Such uniform placement of the wireelectrodes is difficult to achieve when the target tissue volume hasnon-uniform characteristics, such as density, tissue type, structure,and other discontinuities which could deflect the path of a wire as itis advanced through the tissue.

Of particular interest to the present invention, as recognized by theinventor herein, difficulties have arisen in using the multipleelectrode arrangements of WO 96/29946 in treating tumors which lay at ornear the surface of an organ, such as the liver. As illustrated in FIG.1, a LeVeen™ Needle Electrode used for treating a tumor T near thesurface S of a liver L can result in at least some of the tips ofelectrodes 12 emerging from the surface. Such exposure of the needletips outside of the liver is disadvantageous in a number of respects.First, the presence of active electrodes outside of the confinement ofthe organ being treated subjects other tissue structures of the patientas well as the treating personnel to risk of accidental contact with theelectrodes. Moreover, the presence of all or portions of particularelectrodes outside of the tissue being treated can interfere with properheating of the tissue and control of the power supply driving theelectrodes. While it would be possible to further penetrate the needleelectrode 10 into the liver tissue, such placement can damage excessiveamounts of healthy liver. Moreover, the heating characteristics of theliver tissue near the surface will be different from those of livertissue away from the surface, rendering proper treatment of the tumortissue near the surface difficult even if the electrodes are not exposedabove the surface.

In addition to difficulties in treating lesions near the surface of anorgan, electrosurgical probes for performing large volume tissueablation can have difficulty in treating highly vascularized tissuesand/or tissue near a large blood vessel. In both cases, heat beingintroduced by the electrode can be rapidly carried away by the blood,making the heating and control of temperature in the tissue difficult.

For all of these reasons, it would be desirable to provide improvedelectrosurgical methods and systems for treating tumors which lie at ornear the surface of an organ or tissue mass. It would be furtherdesirable to provide such improved methods and systems which would becapable of improving beat transfer into and/or temperature uniformity ofvascularized tissues where the heat can be taken away by blood flow. Itwould be particularly desirable if such methods and systems could lessenthe risk of accidental exposure of the treating electrodes above thetissue surface. It would be further desirable if the methods and systemswould enhance uniform treatment of the entire tumor mass, includingthose portions which lie near the surface of the organ being treated.Still further, it would be desirable if the methods and systems couldachieve treatment of irregularly shaped tumors and tumors which extendfrom an organ surface to relatively deep within the organ. At least someof these objectives will be met by the invention of the presentapplication.

2. Description of the Background Art

WO 96/29946 describes an electrosurgical probe having deployableelectrode elements of the type described above. The LeVeen™ NeedleElectrode constructed in accordance with the teachings of WO 96/229946is available from Radio Therapeutics Corporation, assignee of thepresent application, and is illustrated in brochure RTC 002 published in1998. Other electrosurgical devices having deployable electrodes aredescribed in German Patent 2124684 (Stadelmayr); U.S. Pat. Nos.5,472,441 (Edwards et al.); 5,536,267 (Edwards et al.); and 5,728,143(Gough et al.); and PCT Publications WO 97/06739; WO 97/06740; WO97/06855; and WO 97/06857. Medical electrodes having pins and otherstructures are shown in U.S. Pat. Nos. 3,991,770; Re. 32,066; 4,016,886;4,140,130; 4,186,729; 4,448,198; 4,651,734; and 4,969,468. A skinsurface treatment electrode for the removal of blemishes having acircular array of tissue-penetrating pins is described in Rockwell, TheMedical and Surgical Uses of Electricity, E. B. Trent & Co., New York,1903, at page 558. A cluster electrode comprising a plurality ofelectrodes projecting from a plate for insertion in tissue is describedin WO 99/0410.

SUMMARY OF THE INVENTION

The present invention provides improved methods, systems, and kits forperforming electrosurgical treatment of tumors and other diseaseconditions within body organs and other tissue masses. The methods,systems, and kits are particularly useful for treating tumors which lieat or near the surface of an organ, such as the liver, kidney, pancreas,stomach, spleen, particularly the liver. In a first aspect, the presentinvention relies on applying electrical energy, such as radiofrequencyor other high frequency energy, to or between an internal tissue siteand an external tissue site on the surface of the organ. The energy maybe applied in a monopolar fashion where the internal and external sitesare maintained at the same polarity and a dispersive or passiveelectrode disposed on the patient's skin is maintained at the oppositepolarity. The high frequency energy can be applied simultaneously toboth the internal and external sites, but will more usually be appliedsequentially to one site and then to the other. The energy may also beapplied in a bipolar fashion where the internal treatment site ismaintained at one polarity and the external treatment site maintained atthe opposite polarity. Monopolar treatment is advantageous in permittingformation of two fully formed lesions (necrosed regions) that can beoverlapped to treat a desired region, but is disadvantageous since itrequires use of a dispersive electrode. Bipolar treatment eliminates theneed for a dispersive electrode and, by proper spacing, permitsformation of a single, continuous lesion. Such approaches reduce therisk of passing internally deployed electrode(s) out through the surfaceof the body organ and enhances the uniform electrosurgical treatment oftissue between the internal and exterior treatment sites.

In a second aspect, the present invention provides for applyingelectrical energy, such as radiofrequency or other high frequencyenergy, to an internal tissue site while a cover is deployed over thetissue surface adjacent to the target region within the tissue which isbeing treated. The cover may comprise electrode(s) as described above.Alternatively, the cover may be electrically neutral (unpowered) and/orelectrically insulated to protect surrounding tissue and treatingpersonnel, as described above. Such covers should be capable ofcompressing the tissue in order to inhibit blood flow to and from thetarget region being treated. By inhibiting blood flow, energy losses canbe minimized and temperature uniformity enhanced. The covers may berigid plates, conformable surfaces, or the like, and will typically beclipped or otherwise removably or positionably attached to a primarytreatment probe. In addition to being electrically insulated, the coverwill preferably also be thermally insulating to protect adjacent tissuestructures from thermal damage and further to inhibit heat losses fromthe tissue which is being treated. While in some instances the cover maybe discontinuous, i.e., perforated or having other openings orapertures, it will usually be desirable to utilize a cover having acontinuous surface which can inhibit the loss of steam from the tissuewhich is being treated. Containment of steam within the region beingtreated further enhances tissue heating. Preferably, the compressiveforce between a deployed electrode array on the primary treatment probeand the cover on the tissue surface will be in the range from 0.5 psi to1.5 psi, preferably 0.8 psi to 1.2 psi.

A method according to the present invention for treating a target regionbeneath a tissue surface, such as a tumor site closely beneath thesurface of an organ, comprises deploying a first array of electrodes inthe tissue at or near the target region, preferably being distal to thesite. A second electrode is deployed on the tissue surface over thetarget region, and an electrical current, typically radio or other highfrequency current, is then applied to the tissues through theelectrodes. The current may be applied in a monopolar fashion, i.e. withthe first array of electrodes and the second electrode beingsimultaneously and/or successively connected to one pole of a powersource and a dispersive or passive electrode disposed on the patient'souter skin attached to the other pole. Alternatively, the first array ofelectrodes and the second electrode may be powered in a bipolar fashionby attaching them to opposite poles of the power supply.

The first array of electrodes is preferably deployed by positioning aprobe so that a portion of the probe lies near the target region in thetissue to be treated. A plurality of at least three array electrodes isthen advanced radially outwardly from the probe to define the firstelectrode array. The probe may be advanced directly into tissue, e.g.using a sharpened distal tip on the probe itself, or may be introducedtogether with a stylet which is then removed in order to permitintroduction of the electrodes through the probe. Conveniently, theprobe for deploying the electrode array may be constructed similarly oridentically to a LeVeen™ Needle Electrode as described in WO 96/29946.With such LeVeen™ Needle Electrodes, the electrodes advance initially inthe forward direction and then evert (i.e. follow an arcuate path fromthe tip of the probe) outwardly as they are further advanced into thetissue. The electrodes will preferably deploy outwardly to span a radiusof from 0.5 cm to 3 cm when the individual electrode elements are fullyextended. The array electrodes may be deployed at a depth below thetissue surface in the range from 2 cm to 10 cm, preferably from 3 cm to5 cm, (based on the position of the probe tip), with all individualelectrode elements preferably lying completely within tissue.

The second electrode may comprise a plate or other electrode structurewhich is engaged directly against the tissue surface. The plate or otherstructure will usually have an active electrode area in the range from 3cm² to 15 cm², preferably from 5 cm² to 10 cm². The second electrode mayfurther comprise a plurality of tissue-penetrating electrode elementswhich penetrate into the tissue when the second electrode is engagedagainst the tissue surface. The tissue-penetrating electrode elementswill usually be distributed over an area as set forth above for theplate electrode, and will preferably be capable of being penetrated to adepth below the tissue surface in the range from 3 mm to 10 mm,preferably from 4 mm to 6 mm. The tissue-penetrating elements willusually be parallel to each other, more usually being normal orperpendicular to a planar support plate, and are preferably pins havinga diameter in the range from 1 mm to 3 mm, preferably from 1.5 mm to 2mm, and a length sufficient to provide the tissue penetration depths setforth above. Optionally, the second electrode can be attached to theprobe after the first electrode array has been advanced and deployedbeneath the tissue. By attaching the second electrode to the probe, theentire system can be immobilized while the target region is beingtreated.

The active electrode area of both the first electrode array and secondelectrode will be the surface area of the electrode structure which isexpected to come into contact with tissue in order to transferelectrical current. The total active electrode area of the first arrayof electrodes will typically be in the range from 1 cm² to 5 cm²,preferably from 2 cm² to 4 cm². The area for the exemplary LeVeen™Needle electrode is about 3 cm². The active electrode area for thesecond electrode will be in the ranges generally set forth above. In thecase of second electrodes having pins projecting from the surface of aplate, the active electrode area may be defined by the pins, the platesurface, or a combination of both. It will be appreciated that portionsof the plate and/or the pins may be covered with electrical and thermalinsulation to achieve desired tissue treatment patterns. Portions of thefirst array of electrodes may also be insulated in order to change theelectrical transfer characteristics. For monopolar operation, there isgenerally no requirement that the electrode areas of the first electrodearray and the second electrode be the same. In the case of bipolaroperation, however, it will generally be desirable that the totalelectrode areas of both the first array of electrodes and the secondelectrode be generally the same, usually differing by no more than 20%,preferably differing by no more than 10%.

In an alternative method according to the present invention, control ofheat-mediated necrosis of a target region in tissue may be improved byinhibiting blood flow into the target region prior to the heattreatment. Large volume ablation and necrosis of highly vascularizedtissue, such as liver tissue, can be difficult because of thermaltransport from the region due to local blood flow. That is, blood flowthrough the tissue carries heat away. Moreover, because the degree ofvascularization in any particular region is unpredictable, the totalamount of heat which must be delivered in order to effectively necrosethe tissue is difficult to predict. Heat-mediated tissue necrosis maythus be improved by inhibiting blood flow into the treatment regionprior to heating. In some instances, it may be possible to tie off orclamp blood vessels(s) going into the region. Other known techniques forinhibiting blood flow and consequent heat loss include lowering bloodpressure to reduce blood flow in all regions of the body. For thermaltreatment according to the present invention, however, it will bepreferred to first necrose tissue at or near a distal periphery of thetarget region so that the vasculature is at least partly destroyed inorder to reduce the blood flow into the and/or the target region. Mostpreferably, this two-step method will be achieved using the first arrayof electrodes and second electrode as generally described above, wherethe second electrode is first energized to necrose tissue at or near theperiphery of the target region. While this approach is presentlypreferred, it will be appreciated that other heating modalities couldalso be employed, such as microwave heating, dispersed laser energyheating, electrical resistance heating, introduction of heated fluids,and the like.

In a still separate aspect of the methods of the present invention,deployment of the first electrode array and second electrode or othercover in a manner such that tissue is compressed therebetween will(after deployment) also inhibit blood flow into and from the targetregion between the electrodes. Thus, the step of inhibiting blood flowmay be achieved as simply as compressing the tissue in order to reduceblood flow through the target region between the electrodes. Thecompressive forces may be applied by any structure deployed over orotherwise adjacent to the tissue region being treated, usually beingpositioned directly over the target region in the organ being treated.Typically, the primary electrode which is deployed within the tissuewill act as an anchor and the cover or other structure will be securedto a probe or shaft which is part of the electrode. The cover andelectrode can then be drawn together and secured in place to compressall or a portion of the tissue volume being treated. In this way, bloodflow into and out of the region may be significantly decreased.Optionally, such compression is achieved using treatment electrodeswhich are also used for introducing a frequency or other electricalcurrent into the treatment region to effect the heating.

The presence of a cover or second electrode structure can also be reliedon to facilitate deployment of the first electrode array. As discussedabove, the first electrode array is preferably deployed by positioning aprobe so that a portion of the probe lies near the target region in thetissue to be treated. The cover or second electrode structure may beutilized to help initially initial the probe. After determining adesired treatment depth, e.g., based on computed tomography (CT), theposition of the cover or second electrode structure on the probe may befixed so that the distal end of the probe will penetrate tissue to thedesired depth when the cover or second electrode structure engages theupper skin or tissue surface. Thus, the cover or second electrodestructure may be used as a positioning “stop” in the initial deploymentof the probe and first electrode array. After deployment of the firstelectrode array, the cover or second electrode array can optionally bemoved toward the first array and the tissue compressed between the twoas also described above.

While the preferred compression apparatus will use an anchor electrodeand an external compression structure (either electrically active orneutral), it will also be possible to use a pair of spaced-apartstructures penetrated into tissue for compressing the tissuetherebetween. Either or both of the spaced-apart structures may beelectrically active, e.g., acting as energy-applying electrodes forperforming the methods of the present invention. Alternatively, thespaced-apart structures may both be electrically unpowered so that theycompress tissue only and other electrode(s) are used for directingelectrical energy to tissue.

Systems according to the present invention for treating a target regionin tissue beneath the tissue surface comprise a probe having a distalend adapted to be positioned beneath the tissue surface and within orjust proximal to a target region in the tissue. A plurality ofelectrodes are deployable from the distal end of the probe to span aregion of tissue proximate the target region, usually just distal to thesite. The system further includes a cover, such as a surface electrode,adapted to span an area of the tissue surface over the target region.Other exemplary covers include rigid plates, typically in the form of adisc having a generally circular or oval periphery, conformablesurfaces, such as foam layers, polymer discs, deployable electrodestructures having tissue-contacting surfaces, or any other mechanicalstructures which can be deployed over or contacted against tissue toprovide a relatively uniform compressive force against the tissue.Preferably, a surface electrode comprises a support having an electrodeface and an insulated face opposite to the electrode face. In the firstembodiment, the electrode face may be generally flat and have an area inthe ranges set forth above. Alternatively, the surface electrode maycomprise a plurality of tissue-penetrating elements on the face of aplate or other support structure, typically from four tissue-penetratingelements to sixteen tissue-penetrating elements, more preferably fromsix tissue-penetrating elements to nine tissue-penetrating elements.Optionally, the tissue-penetrating elements may be arranged in acircular, grid, concentric ring, serpentine, zig-zag, staggered, orother pattern on the electrode face, further optionally with additionalelectrodes interior to the peripheral electrodes. The tissue-penetratingelements preferably comprise pins having the sizes described above.

The surface electrode may optionally be connected to the probe using aconnector. Usually, the connector will attach the surface electrode in agenerally transverse orientation relative to the axis of the probe.Optionally, the connector can be flexible or in the form of a swivel or“universal joint” which permits the surface electrode to align itselfwith the tissue surface even when the probe is entering at an anglerelative to the tissue surface which is not perpendicular. Othersuitable connectors include clips, pinch clamps, threaded connectors,hook and loop fasteners (such as VELCRO™ brand fasteners), and the like.The connectors should allow the surface electrode or other cover to beselectively attached at various points along the length of the probe.Optionally, the probe can be marked with indicia indicating the depth ofpenetration, i.e., length between the distal tip of the probe and theparticular point on the probe where the surface electrode or other covermay be attached. The ability to connect the surface electrode or othercover to the probe prior to deployment of the first electrode array isuseful in helping to position the probe at a desired treatment depth, asdescribed elsewhere herein.

The surface electrode and the probe may be electrically isolated fromeach other or may be electrically coupled to a common pole for monopolaroperation. For simultaneous monopolar operation, the surface electrode(and any tissue-penetrating elements thereon) will be electricallycoupled to the deployable electrode array on the probe so that all ofthe electrodes in the system can be connected to one pole of anelectrode surgical power supply. Alternatively, the array electrodes onthe probe may be electrically isolated from the second electrode and anytissue-penetrating elements thereon. When electrically isolated, theelectrode array and surface electrode can be driven separately (one at atime) in a monopolar fashion or simultaneously in a bipolar fashion,i.e. each connected to the opposite pole of an electrosurgical powersupply.

The probe will usually comprise a cannula having a proximal end, adistal end, and a lumen extending to at least the distal end. Thedeployable electrodes are resilient and disposed within the cannulalumen to reciprocate between a proximally retracted position where allelectrodes are radially constrained within the lumen and the distallyextended where all electrodes deploy radially outwardly. Usually, theelectrodes will have a shape memory which will deflect the electrodesradially outwardly as they extend from the cannula. The most preferredconfiguration for the deployable electrodes is arcuate so that theyassume an outwardly everted configuration as they are extended from thecannula. Usually, the array electrodes are connected to a rod structurewhich is reciprocatably received in the cannula lumen. Optionally, astylet may be provided as part of the system for placement in thecannula so that a sharpened tip of the cannula extends beyond the distaltip of the cannula. The cannula and stylet may then be introduced to thetarget region through tissue, after which the stylet is removed leavingthe lumen for receiving the electrode array. Usually, the cannula willhave a length in the range from 5 cm to 30 cm, preferably from 12 cm to25 cm, and an outer diameter in the range from 1 mm to 5 mm, usuallyfrom 1.5 mm to 2 mm. The electrode array will deploy outwardly to aradius in the range from 0.5 cm to 3 cm, preferably from 1 cm to 2 cmwhen fully extended. The electrode array will include at least 5electrodes, preferably including at least 8 electrodes and oftenincluding 10 or more electrodes.

Kits according to the present invention will comprise at least a secondelectrode, together with instructions for use for deploying an electrodearray in tissue and engaging the second electrode on a tissue surfaceabove the deployed electrode array for treating a tumor or other diseasecondition at or near the tissue surface. Usually, the second electrode(optionally together with a first electrode array) will be packaged in aconventional medical device package, such as a tray, box, tube, pouch,or the like. The instructions for use may be provided on a separatesheet of paper or may be printed in whole or in part on a portion of thepackaging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates deployment of the prior art LeVeen™ Needle Electrodearray for treatment of a tumor region near the surface of a liver, withseveral of the electrode tips being shown exposed.

FIG. 2 illustrates and improved system according to the presentinvention comprising deployable electrode array, such as the LeVeen™Needle Electrode, in combination with a surface electrode assembly.

FIG. 2A illustrates a cover structure which can be used in place of thesurface electrode assembly illustrated in FIG. 2.

FIG. 3 is a detailed illustration of the distal end of the electrodearray of FIG. 2, shown with the electrode array fully deployed.

FIG. 4 is a side, cross-sectional view of the surface electrode that thesystem of FIG. 2.

FIG. 5 is a bottom view of the surface electrode of the system of FIG.2.

FIGS. 6A-6C illustrates the system of FIG. 2 being used for treatment ofa surface tumor in a monopolar configuration.

FIG. 7 illustrates the system of FIG. 2 connected for treatment of asurface tumor in a bipolar configuration.

FIG. 8 illustrates a kit according to the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Systems according to the present invention are designed to positionelectrode elements and assemblies within and over a treatment regionwithin solid tissue of a patient. The treatment region may be locatedanywhere in the body where hyperthermic exposure may be beneficial. Mostcommonly, the treatment region will comprise a solid tumor within anorgan of the body, such as the liver, kidney, pancreas, breast, prostate(not accessed via the urethra), and the like. The volume to be treatedwill depend on the size of the tumor or other lesion, typically having atotal volume from 1 cm³ to 150 cm³, usually from 1 cm³ to 50 cm³, andoften from 2 cm³ to 35 cm³. The peripheral dimensions of the treatmentregion may be regular, e.g. spherical or ellipsoidal, but will moreusually be irregular. The treatment region may be identified usingconventional imaging techniques capable of elucidating a target tissue,e.g. tumor tissue, such as ultrasonic scanning, magnetic resonanceimaging (MRI), computer-assisted tomography (CAT), fluoroscopy, nuclearscanning (using radiolabeled tumor-specific probes), and the like.Preferred is the use of high resolution ultrasound which can be employedto monitor the size and location of the tumor or other lesion beingtreated, either intraoperatively or externally.

Of particular interest to the present invention, tumors and othertreatment regions which lie at or near the surface of a body organ orother tissue mass may be effectively treated by deploying a first arrayof electrodes in the tissue at or within the target region, typicallybeing positioned at the posterior periphery of the region to be treated,and deploying a cover or a second electrode on the tissue surface overthe target region. The cover can be any structure which can be securedto the first array of electrodes in order to cover and/or compresstissue between the surface and the region in which the first electrodeis being deployed. In a first instance, the cover will not be used forimparting electrical energy, usually being at least partly formed fromor covered by an electrically and/or thermally insulating material. Insuch instances, the cover will only act to isolate and/or compress thetissue. In other cases, the cover will be in the form of a secondelectrode as described below. The second electrode may be a generallyplanar electrode but will preferably comprise a plurality oftissue-penetrating electrode elements which can penetrate through thetissue surface to provide effective electrical coupling and currentdistribution to the tissue being treated. By then applying electricalcurrent, usually radio or other high frequency current, to the tissuethrough the first array of electrodes and the second electrode,sequentially or simultaneously, the tissue can be effectively treatedboth at or near the surface as well as at lower depths within the tissueregion.

Systems according to the present invention will usually comprise of aprobe having a distal end adapted to be positioned beneath the tissuesurface at or near the target region or region. A plurality oftissue-penetrating electrodes, typically in the form of sharpened, smalldiameter metal elements are reciprocatably attached to the probe so thatthey penetrate into tissue as they are advanced from a target regionwithin the target region, as described in more detail hereinafter. Theprimary requirement of such electrode elements is that they can bedeployed in an array, preferably a three-dimensional array, emanatinggenerally from a target region within the treatment region of thetissue. In the exemplary embodiment, the electrode elements are firstintroduced to the target region in a radially collapsed or otherconstrained configuration, and thereafter advanced into the tissue froma delivery cannula or other element in a divergent pattern to achievethe desired three-dimensional array. The electrode elements will divergeradially outwardly from the delivery cannula (located at the targetregion) in a uniform pattern, i.e. with the spacing between adjacentelectrodes diverging in a substantially uniform and/or symmetricpattern. Preferably, pairs of adjacent electrodes will be spaced-apartfrom each other in similar or identical, repeated patterns and willusually be symmetrically positioned about an axis of the deliveryelement. The electrode elements may extend or project along generallystraight lines from the target region, but will more usually be shapedto curve radially outwardly and optionally to evert proximally so thatthey face partially or fully in the proximal direction when fullydeployed. It will be appreciated that a wide variety of particularpatterns can be provided to uniformly cover the region to be treated.

The second electrode, also referred to herein as the surface electrode,is intended to provide electrical contact with a region of the tissuesurface which is located generally over the target region with thetissue. When the tumor or other target region extends to the tissuesurface, the second electrode will preferably be positioned to cover allor as much of the exposed tumor as possible. In its simplest form, thesecond electrode may be a generally flat or planar plate electrode, e.g.being a simple disc having an area within the ranges set forthpreviously. Preferably, however, the second electrode will comprise aplurality of tissue-penetrating electrode elements which projectperpendicularly from the electrode plate or other support structure. Thetissue-penetrating electrode elements will form part of the electricallyconductive electrode structure, with the supporting plate or otherstructure being either active or inactive, i.e. the rest of thesupporting structure may be insulated so that it is not electricallyactive when in contact with tissue. In almost all cases, the oppositeface of the electrode structure, i.e. all portions of the electrodewhich are not intended to contact tissue, will be electrically andthermally insulated to prevent accidental tissue contact withelectrically active and heated components of the electrode duringperformance of a procedure. The tissue-penetrating elements may besimple blunt pins, sharpened pins, or needles which projectperpendicularly from the planar electrode support, usually havingdimensions within the ranges set forth above. The number oftissue-penetrating elements on the second electrode will also be withinthe ranges set forth above. The electrically conductive components ofthe second electrode, including all those which come into contact withtissue, will usually be formed from or plated with an electricallyconductive metal, such as stainless steel, gold, silver, brass, and thelike.

The second electrode will preferably be attachable to the probe whichdeploys the first electrode array, usually being attached after thefirst electrode array is deployed. In the exemplary embodiment, thesecond electrode is a disc structure having a central aperture which canbe selectively and slidably positioned over the probe shaft and lockedinto position. In such cases, the second electrode will be disposed in agenerally transverse orientation when the electrode is locked on theprobe. When the second electrode carries tissue-penetrating elements,those elements will usually be aligned in a parallel orientation withthe axis of the probe. In some cases, however, it may be desirable toattach the second electrode so that it is capable of pivoting orotherwise adjusting its planar orientation relative to the axis of theprobe. For example, the second electrode may be attached using aball-and-socket or other universal joint which permits relatively freemovement of the second electrode about the pivot point defined by theattachment to the probe. In the exemplary embodiments, if the tumorbeing treated approaches or reaches the surface of the tissue or organ,the second (surface) electrode may be placed onto the shaft of the probeafter the first electrode array is deployed. Deployment of the firstelectrode array will anchor the distal end of the probe in tissue,permitting the second electrode to be firmly engaged against the tissuesurface, preferably so that tissue between the deployed electrode arrayand the second electrode array and the second electrode will be slightlycompressed. Such compression has at least two advantages. First, bothelectrodes are held firmly in place so that they are less likely tobecome dislodged. More importantly, compression of the tissue tends toinhibit blood flow into the treatment region rendering heating of thetissue more rapid and more controllable. When employingtissue-penetrating elements on the second electrode, it is desirablethat they be fully inserted into the tissue. The depth of tissuepenetration by the elements largely determines the depth of the surfacelesion being created, i.e. the more fully the elements penetrate intotissue, the deeper the lesion will be.

Monopolar operation may be effected in two ways. Most commonly, thefirst electrode array and second electrode will be electrically isolatedfrom each other and powered separately, preferably with the firstelectrode array being powered first in order to necrose tissue at aboundary of the target region and inhibit blood flow into the region. Inother cases, however, if sufficient power is available, the firstelectrode array and second electrode may be driven simultaneously whileattached to a common pole on an electrosurgical power supply. Althoughnot essential, the first electrode array and second electrode may havesimilar available electrode areas, so that approximately the sameheating will occur from both the electrodes simultaneously, but at halfthe power level which will be achieved using the same power level withonly a single electrode.

For bipolar operation, the electrically conductive components of thesecond electrode will be electrically isolated from the electricallyconductive components of the first electrode array. In that way, thesecond electrode and first electrode array can be attached to oppositepoles of a radiofrequency or other power supply in order to effectbipolar current flow between the deployed electrode components.Preferably, the available surface areas of the first electrode array andthe second electrode will be approximately equal so that heating (energytransfer into unit volumes of adjacent tissue) occurs at approximatelythe same rate from both electrode structures. If the areas differsignificantly from each other, the current flux from the smallerelectrode will be denser, which can cause premature desiccation at oneelectrode before the entire target tissue region has been effectivelyheated. Premature desiccation limits the ability of the electrode topass current through the tissue, rendering further treatment difficult.

It will be appreciated that in monopolar operation, a passive ordispersive “electrode” must also be provided to complete the return pathfor the circuit being created. Such electrodes, which will usually beattached externally to the patient's skin, will have a much larger area,typically about 130 cm² for an adult, so that current flux issufficiently low to avoid significant heating and other biologicaleffects. It may also be possible to provide such a dispersive returnelectrode directly on a portion of a sheath, core element, or otherportion of the system of the present invention (generally, when thereturn electrode is on the same sheath or core, the device may still bereferred to as bipolar).

The RF power supply may be a conventional general purposeelectrosurgical power supply operating at a frequency in the range from300 kHz to 1.2 MHz, with a conventional sinusoidal or non-sinusoidalwave form. Such power supplies are available from many commercialsuppliers, such as Valleylab, Aspen, and Bovie. Most general purposeelectrosurgical power supplies, however, operate at higher voltages andpowers than would normally be necessary or suitable for the methods ofthe present invention. Thus, such power supplies will usually beoperated at the lower ends of their voltage and power capabilities. Moresuitable power supplies will be capable of supplying an ablation currentat a relatively low voltage, typically below 150 V (peak-to-peak),usually being from 50 V to 100 V. Such low voltage operation permits useof a power supply that will significantly and passively reduce output inresponse to impedance changes in the target tissue. The power willusually be from 50 W to 200 W, usually having a sine wave form, butother wave forms would also be acceptable. Power supplies capable ofoperating within these ranges are available from commercial vendors,such as Radionics and RadioTherapeutics Corporation. A preferred powersupply is model RF-2000, available from RadioTherapeutics Corporation,Mountain View, Calif., assignee of the present application.

The probe which contains the deployable electrode elements will usuallybe contained by or within an elongate member, typically a rigid orsemi-rigid, metal or plastic cannula. In some cases, the cannula willhave a sharpened tip, e.g. be in the form of a needle, to facilitateintroduction to the tissue target region. In such cases, it is desirablethat the cannula or needle be sufficiently rigid, i.e. have sufficientcolumn strength, so that it can be accurately advanced through tissue.In other cases, the cannula may be introduced using an internal styletwhich is subsequently exchanged for the electrode array. In the lattercase, the cannula can be relatively flexible since the initial columnstrength will be provided by the stylet. The cannula serves to constrainthe individual electrode elements in a radially collapsed configurationto facilitate their introduction to the tissue target region. Theelectrode elements can then be deployed to their desired configuration,usually a three-dimensional configuration, by extending distal ends ofthe electrode elements from the distal end of the cannula into thetissue. In the preferred case of the tubular cannula, this can beaccomplished simply by advancing the distal ends of the electrodeelements distally from the tube so that they emerge and deflect (usuallyas a result of their own spring or shape memory) in a radially outwardpattern. Alternatively, some deflection element or mechanism could beprovided on the elongate member to deflect members with or without shapememory in a desired three-dimensional pattern.

Referring to FIGS. 2-5, an exemplary electrode deployment system 20constructed in accordance with the principles of the present invention.The system 20 comprises a probe 22 and a surface electrode 24. The probe22 will be generally as described above, and will preferably be aLeVeen™ Needle Electrode of the type which is available fromRadioTherapeutics Corp., Mountain View, Calif., assignee of the presentapplication. The probe 22 comprises a handle 26 and a cannula 28, wherethe cannula has a sharpened distal tip 30 which may be directlyintroduced through tissue to a target region. As best observed in FIG.3, a plurality of everting electrodes 32 may be deployed from the tip 30by advancing a button 34 on the handle. The everting electrodes 32 areelectrically coupled to a connector 40 (FIG. 2) at the proximal end ofthe handle 22 through a shaft 42 which is used to deploy the electrodes.The outer surface of the cannula 28 will be insulated so that currentflows only through the everted electrodes 32 and the surface electrode24.

As alternative to the second or surface electrode 24, a cover 25 may beused, as illustrated in FIG. 2A. The cover is not configured to act asan electrode and will usually be free from tissue-penetratingcomponents. The cover will usually be disc-shaped and will generallyhave the dimensions of the electrode array 24. Unlike electrode array24, however, the cover will not be intended for use as an electrode.Usually, at least a portion of the cover will be electrically and/orthermally insulating, i.e., formed from an electrically and/or thermallyinsulating material or covered by an insulator. Preferably, the coverwill be both electrically and thermally insulating. Conveniently, theentire disc may be formed from a polymer, ceramic, or other materialhaving a high electrical impedance to help isolate the region beingtreated and prevent accidental contact with the electrodes of array 30deployed beneath the tissue surface. Usually, a clip or other fasteningstructure (not shown) will be provided on the cover 25 to permitselective mounting, positioning, and removal on to the shaft 28 of thesystem 20. A variety of suitable connectors have been describedelsewhere herein.

As best observed in FIGS. 4 and 5, the surface electrode 24 comprises anelectrically conductive plate 50 having a plurality oftissue-penetrating pin electrodes 52 projecting forwardly from face 56thereof. Preferably, the pin electrodes 52 will project in a generallyperpendicular direction from the planar face 56. Usually, but notnecessarily, face 56 will be covered with an insulating layer so thatelectrical contact is made through only the pins 52. In some cases,however, it may be desirable to leave the face 56 uninsulated so thatelectrical contact can be made through the face as well. A slot 60 isformed in the plate 50 so that the surface electrode 24 may be mountedonto the cannula 28 as seen in FIG. 2. An enlarged central aperture 62may be provided for locking on to the cannula. Alternative lockingmechanisms may also be provided, such as compression locks, latches, andthe like (not illustrated) which permit axial movement of the surfaceelectrode 24 along the length of cannula 28 and selective locking of thesurface electrode at a desired position. Optionally, a collar 64 may beprovided on the opposite face 70 of the plate to assist in holdingand/or locking of the surface electrode 24 on the cannula 28.Preferably, electrical and thermal insulating layers 72 will be providedover all exposed portions of the surface electrode so that the chance ofaccidental contact between the surface electrode and other tissuestructures near the treatment region is minimized. It will beappreciated that the surface electrode 24 may be attached at virtuallyany axial location along the cannula 28 so that the distance between thesurface electrode and the distal tip (electrode deployment point) 30 ofthe probe 22 can be fully adjusted. Also, as described above, theconnection between the cannula 28 and the surface electrode 24 can bemade to freely pivot so that the electrode can adjust to differentsurface orientations of the tissue after the cannula 28 has beenintroduced into tissue.

Referring now to FIGS. 6A-6C, monopolar operation of the electrodesystem 20 will be described. After imaging the tumor or other treatmentregion T in the liver L, the cannula 28 is introduced through the tissuesurface F until the distal tip 30 advances to point generally at theposterior of the tumor region T. The electrodes 32 are then deployed byadvancing them out of the distal tip 30, and the surface electrode 24placed on to the cannula 28. The surface electrode 24 is then advancedtoward the tissue surface S so that the electrode pins 52 advance intothe tissue, and more particularly into the treatment region T, asillustrated in FIG. 6A. Current may then be applied in either of the twogeneral modes described above. In a first mode (not illustrated) thesurface electrode 24 and deployed electrodes are powered simultaneouslyto treat the entire target region T at once. In the illustrated andpresently preferred mode, however, the deployed electrodes 32 are firstenergized to necrose a boundary region B1, as generally shown in FIG.6B. Necrosis of the boundary region B1 will not only treat a significantportion of the tissue within the target region T, it will also at leastpartially inhibit blood flow into and from the target region tofacilitate subsequent treatment with the surface electrode 24. After thefirst treatment step using deployed electrodes 32 is completed, thesurface electrode 24 will be separately powered in order to treat asecond boundary region B2 as shown in FIG. 6C. Preferably, these regionswill at least partially overlap, and more preferably will completelyoverlap in order to fully necrose the treatment region T.

Bipolar treatment according to the present invention is effected inmanner very similar to that described for monopolar treatment. As shownin FIG. 7, electrodes 32 and surface electrode 24 are deployed on eitherside of the treatment region T. The electrodes 32 and 24 will, however,be electrically isolated from each other. A first pole of the powersupply 100 is then coupled to the electrodes 32 of the interiorelectrode array while the second pole of the power supply is connectedto the surface electrode 24. Radio or other high frequency energy canthen be applied to the tissue in a bipolar fashion where current flowsbetween the electrodes 32 and surface electrode 24, with the currentflux being localized generally within the tumor or other treatmentregion T.

Referring now to FIG. 8, a kit according to the present invention willcomprise at least a surface electrode 24, optionally a probe 20, andinstructions for use IFU. The probe 20 and surface electrode 24 may begenerally as described above, and the instructions for use will setforth a method for employing the probe 20 and the surface electrode 24in accordance with any of the methods of the present invention describedabove. The instructions for use will generally be written on a packageinsert or other separate piece of paper 150, but may also be printed inwhole or in part on the packing materials. Usually, all components ofthe kit will be packaged together in a conventional package 160, such asa pouch, tray, box, tube, or the like. Preferably, all system componentswill be sterilized within the package so that they are immediately readyfor use in the sterile environment.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

What is claimed is:
 1. A method for treating a target region in tissueat or beneath a tissue surface, said method comprising: deploying afirst array of electrodes in the tissue beneath the tissue surface atthe target region; deploying a second electrode on the tissue surfaceover the target region; and applying electrical current to the tissuethrough the electrodes.
 2. A method as in claim 1, wherein the highfrequency current is applied successively from the electrodes in amonopolar mode.
 3. A method as in claim 1, wherein high frequencycurrent is applied with one pole attached to the array electrodes andanother pole attached to the second electrode in a bipolar fashion.
 4. Amethod as in claim 1, wherein deploying the second electrode comprisesengaging a plate electrode against the tissue surface.
 5. A method as inclaim 4, wherein the plate electrode has an area in the range from 2 cm²to 10 cm².
 6. A method as in claim 1, wherein deploying the secondelectrode comprises penetrating a plurality of tissue-penetratingelectrode elements through the tissue surface.
 7. A method as in claim6, wherein the plurality of tissue-penetrating electrode elements arepenetrated over an area in the range from 2 cm² to 10 cm².
 8. A methodas in claim 7, wherein the electrode elements are penetrated to a depthin the range from 3 mm to 10 mm.
 9. A method as in claim 1, wherein highfrequency current is applied simultaneously through both the arrayelectrodes and the second electrode attached to a common pole of a powersupply in a monopolar mode.
 10. A method as in claim 6, wherein thetissue-penetrating electrode elements are pins having a diameter in therange from 1 mm to 3 mm and a depth from the electrode face in the rangefrom 3 mm to 10 mm.
 11. A method for treating a target region in tissueat or beneath a tissue surface, said method comprising: deploying afirst array of electrodes in the tissue beneath the tissue surface atthe target region; deploying a cover over the tissue surface over thetarget region, wherein the cover is configured to electrically andthermally isolate the target region and first electrode array fromexternal tissue structures adjacent to the target region; and applyingelectrical current to tissue in the target region through the firstarray of electrodes.
 12. A method as in any of claims 1, 2, or 11,wherein deploying the first 2 array of electrodes comprises: positioninga probe so that a portion of the probe is near the target region in thetissue; and advancing a plurality of at least three array electrodesradially outwardly from the probe to define the first electrode array.13. A method as in claim 12, wherein the probe is advanced directly intotissue with the array electrodes retracted within the probe.
 14. Amethod as in claim 12, wherein a combination of probe and stylet isinitially advanced into the tissue, and wherein the stylet is withdrawnfrom the probe prior to advancing the array electrodes through theprobe.
 15. A method as in claim 12, wherein advancing the arrayelectrodes comprises advancing them forwardly from a distal end of theprobe so that the electrodes evert outwardly as they are advanced intothe tissue.
 16. A method as in claim 12, wherein the array electrodesdeploy outwardly to a radius from 0.5 cm to 3 cm when fully distallyextended.
 17. A method as in claim 12, further comprising removablyattaching the second electrode to the probe after the array electrodeshave been advanced.
 18. A method as in any of claims 1, 2, or 3, whereinthe first array electrodes are deployed at a depth below the tissuesurface in the range from 2 cm to 10 cm.
 19. A method for treating atarget region in tissue at or beneath a tissue surface, said methodcomprising: deploying a first array of electrodes in the tissue beneaththe tissue surface at the target region; deploying a cover over thetissue surface over the target region, wherein the first array and coverare drawn together to apply compression on tissue in the target region;and applying electrical current to tissue in the target region throughthe first array of electrodes.
 20. A method as in claim 19, wherein theelectrical current is applied first through the first array ofelectrodes to necrose tissue at or near a boundary of the target regionto inhibit blood flow into the target region.
 21. A method as in claim19 or 11, wherein the cover comprises a rigid plate.
 22. A method as inclaim 19 or 11, wherein the cover comprises a conformable surface.
 23. Amethod as in claim 19 or 11, wherein the cover is composed of anelectrically non-conductive material.
 24. A method as in claim 19 or 11,wherein the cover and first electrode array are drawn together with aforce of at least 0.5 psi.
 25. A method as in claim 19 or 11, whereindeploying the first electrode array comprises positioning a probe sothat a portion of the probe lies near the target region and deployingthe cover comprises securing the cover to the probe after the probe hasbeen deployed.
 26. A method for treating a target region in tissue at orbeneath a tissue surface, said method comprising: deploying a firstarray of electrodes in the tissue at the target region; penetrating aplurality of tissue-penetrating electrodes comprising a second electrodearray through the tissue surface; applying electrical current to thetissue through the electrodes.
 27. A method as in claim 26, whereindeploying the first array of electrodes comprises: positioning a probeso that a portion of the probe is near the target region in the tissue;and advancing a plurality of at least three array electrodes radiallyoutwardly from the probe to define the first electrode array.
 28. Amethod as in claim 27, wherein the probe is advanced directly intotissue with the array electrodes retracted within the probe.
 29. Amethod as in claim 27, wherein a combination of probe and stylet isinitially advanced into the tissue, and wherein the stylet is withdrawnfrom the probe prior to advancing the array electrodes through theprobe.
 30. A method as in claim 27, wherein advancing the arrayelectrodes comprises advancing them forwardly from a distal end of theprobe so that the electrodes evert outwardly as they are advanced intothe tissue.
 31. A method as in claim 27, wherein the array electrodesdeploy outwardly to a radius from 0.5 cm to 3 cm wherein fully distallyextended.
 32. A method as in claim 27, further comprising removablyattaching the second electrode to the probe after the array electrodeshave been advanced.
 33. A method as in claim 26, wherein the first arrayelectrodes are deployed at a depth below the tissue surface in the rangefrom 2 cm to 10 cm.
 34. A method as in claim 26, wherein penetrating thesecond electrode comprises engaging a plate electrode against the tissuesurface.
 35. A method as in claim 34, wherein the plate electrode has anarea in the range from 2 cm² to 10 cm².
 36. A method as in claim 26,wherein the plurality of tissue-penetrating electrode elements arepenetrated over an area in the range from 2 cm² to 10 cm².
 37. A methodas in claim 26, wherein the electrode elements are penetrated to a depthin the range from 3 mm to 10 mm.
 38. A method as in claim 26, whereinthe tissue-penetrating electrode elements are pins having a diameter inthe range from 1 mm to 3 mm and a depth from an electrode face in therange from 3 mm to 10 mm.
 39. A method as in claim 26, wherein highfrequency current is applied simultaneously through both the arrayelectrodes and the second electrode attached to a common pole of a powersupply in a monopolar mode.
 40. A method as in claim 26, wherein highfrequency current is applied with one pole attached to the arrayelectrodes and another pole attached to the second electrode in abipolar fashion.
 41. A method as in claim 26, wherein the high frequencycurrent is applied successively from the electrodes in a monopolar mode.42. A method for treating a target region in tissue at or beneath atissue surface, said method comprising: positioning a probe so that aportion of the probe is near the target region in tissue; advancing aplurality of at least three array electrodes radially outwardly from theprobe to define a first electrode array; deploying a second electrode onthe tissue surface over the target region; removably attaching thesecond electrode to the probe after the first array electrodes have beenadvanced; and applying electrical current to the tissue through theelectrodes.
 43. A method for treating a target region in tissue at orbeneath a tissue surface, said method comprising: positioning a probe sothat a portion of the probe is near the target region in tissue;advancing a plurality of at least three array electrodes radiallyoutwardly from the probe to define a first electrode array; deploying acover over the tissue surface over the target region, wherein the firstarray and cover are drawn together to apply compression on tissue in thetarget region; removably attaching the second electrode to the probeafter the first array electrodes have been advanced; and applyingelectrical current to tissue in the target region through the firstarray of electrodes.
 44. A method for treating a target region in tissueat or beneath a tissue surface, said method comprising: positioning aprobe so that a portion of the probe is near the target region intissue; advancing a plurality of at least three array electrodesradially outwardly from the probe to define a first electrode array;deploying a cover over the tissue surface over the target region,wherein the cover is configured to electrically and thermally isolatethe target region and first electrode array from external tissuestructures adjacent to the target region; removably attaching the secondelectrode to the probe after the first array electrodes have beenadvanced; and applying electrical current to tissue in the target regionthrough the first array of electrodes.
 45. A method as in any of claims42, 43, and 44, wherein the probe is advanced directly into tissue withthe array electrodes retracted within the probe.
 46. A method as in anyof claims 42, 43, and 44, wherein a combination of probe and stylet isinitially advanced into the tissue, and wherein the stylet is withdrawnfrom the probe prior to advancing the array electrodes through theprobe.
 47. A method as in any of claims 42, 43, and 44, whereinadvancing the array electrodes comprises advancing them forwardly from adistal end of the probe so that the electrodes evert outwardly as theyare advanced into the tissue.
 48. A method as in any of claims 42, 43,and 44, wherein the array electrodes deploy outwardly to a radius from0.5 cm to 3 cm wherein fully distally extended.
 49. A method as in anyof claims 42, 43, and 44, wherein the first array electrodes aredeployed at a depth below the tissue surface in the range from 2 cm to10 cm.
 50. A method as in claim 42, wherein deploying the secondelectrode comprises engaging a plate electrode against the tissuesurface.
 51. A method as in claim 42, wherein the plate electrode has anarea in the range from 2 cm² to 10 cm².
 52. A method as in claim 42,wherein deploying the second electrode comprises penetrating a pluralityof tissue-penetrating electrode elements through the tissue surface. 53.A method as in claim 52, wherein the plurality of tissue-penetratingelectrode elements are penetrated over an area in the range from 2 cm²to 10 cm².
 54. A method as in claim 53, wherein the electrode elementsare penetrated to a depth in the range from 3 mm to 10 mm.
 55. A methodas in claim 52, wherein the tissue-penetrating electrode elements arepins having a diameter in the range from 1 mm to 3 mm and a depth froman electrode face in the range from 3 mm to 10 mm.
 56. A method as inclaim 42, wherein high frequency current is applied simultaneouslythrough both the array electrodes and the second electrode attached to acommon pole of a power supply in a monopolar mode.
 57. A method as inclaim 42, wherein high frequency current is applied with one poleattached to the array electrodes and another pole attached to the secondelectrode in a bipolar fashion.
 58. A method as in claim 42, wherein thehigh frequency current is applied successively from the electrodes in amonopolar mode.
 59. A method as in claim 43, wherein the high frequencycurrent is applied first through the first array of electrodes tonecrose tissue at or near a boundary of the target region to inhibitblood flow into the target region.
 60. A method as in claim 43 or 44,wherein the cover comprises a rigid plate.
 61. A method as in claim 43or 44, wherein the cover comprises a conformable surface.
 62. A methodas in claim 43 or 44, wherein the cover is composed of an electricallynon-conductive material.
 63. A method as in claim 43 or 44, wherein thecover and first electrode array are drawn together with a force of atleast 0.5 psi.
 64. A method as in claim 43 or 44, wherein deploying thefirst electrode array comprises positioning a probe so that a portion ofthe probe lies near the target region and deploying the cover comprisessecuring the cover to the probe after the probe has been deployed.
 65. Amethod for treating a target region in tissue at or beneath a tissuesurface, said method comprising: deploying a first array of electrodesin the tissue at the target region; deploying a cover composed of anelectrically non-conductive material over the tissue surface over thetarget region, wherein the first array and cover are drawn together toapply compression on tissue in the target region; and applyingelectrical current to tissue in the target region through the firstarray of electrodes.
 66. A method for treating a target region in tissueat or beneath a tissue surface, said method comprising: deploying afirst array of electrodes in the tissue at the target region; deployinga cover composed of an electrically non-conductive material over thetissue surface over the target region, wherein the cover is configuredto electrically and thermally isolate the target region and firstelectrode array from external tissue structures adjacent to the targetregion; and applying electrical current to tissue in the target regionthrough the first array of electrodes.
 67. A method as in claim 65 or66, wherein deploying the first array of electrodes comprises:positioning a probe so that a portion of the probe is near the targetregion in the tissue; and advancing a plurality of at least three arrayelectrodes radially outwardly from the probe to define the firstelectrode array.
 68. A method as in claim 67, wherein the probe isadvanced directly into tissue with the array electrodes retracted withinthe probe.
 69. A method as in claim 67, wherein a combination of probeand stylet is initially advanced into the tissue, and wherein the styletis withdrawn from the probe prior to advancing the array electrodesthrough the probe.
 70. A method as in claim 67, wherein advancing thearray electrodes comprises advancing them forwardly from a distal end ofthe probe so that the electrodes evert outwardly as they are advancedinto the tissue.
 71. A method as in claim 67, wherein the arrayelectrodes deploy outwardly to a radius from 0.5 cm to 3 cm whereinfully distally extended.
 72. A method as in claim 66 or 67, wherein thefirst array electrodes are deployed at a depth below the tissue surfacein the range from 2 cm to 10 cm.
 73. A method as in claim 67, furthercomprising removably attaching the second electrode to the probe afterthe array electrodes have been advanced.
 74. A method as in claim 65,wherein an high frequency current is applied first through the firstarray of electrodes to necrose tissue at or near a boundary of thetarget region to inhibit blood flow into the target region.
 75. A methodas in claim 65 or 66, wherein the cover comprises a rigid plate.
 76. Amethod as in claim 65 or 66, wherein the cover comprises a conformablesurface.
 77. A method as in claim 65 or 66, wherein the cover and firstelectrode array are drawn together with a force of at least 0.5 psi. 78.A method as in claim 65 or 66, wherein deploying the first electrodearray comprises positioning a probe so that a portion of the probe liesnear the target region and deploying the cover comprises securing thecover to the probe after the probe has been deployed.
 79. A method fortreating a target region in tissue at or beneath a tissue surface, saidmethod comprising: deploying a first array of electrodes from a probe inthe tissue at the target region so that a portion of the probe lies nearthe target region; securing a cover to the probe after the probe hasbeen deployed so that the probe lies over the tissue surface over thetarget region, wherein the first array and cover are drawn together toapply compression on tissue in the target region; and applyingelectrical current to tissue in the target region through the firstarray of electrodes.
 80. A method for treating a target region in tissueat or beneath a tissue surface, said method comprising: deploying afirst array of electrodes from a probe in the tissue at the targetregion so that a portion of the probe lies near the target region;securing a cover to the probe after the probe has been deployed so thatthe probe lies over the tissue surface over the target region, whereinthe cover is configured to electrically and thermally isolate the targetregion and first electrode array from external tissue structuresadjacent to the target region; and applying electrical current to tissuein the target region through the first array of electrodes.
 81. A methodas in claim 79 or 80, wherein deploying the first array of electrodescomprises: positioning a probe so that a portion of the probe is nearthe target region in the tissue; and advancing a plurality of at leastthree array electrodes radially outwardly from the probe to define thefirst electrode array.
 82. A method as in claim 81, wherein the probe isadvanced directly into tissue with the array electrodes retracted withinthe probe.
 83. A method as in claim 81, wherein a combination of probeand stylet is initially advanced into the tissue, and wherein the styletis withdrawn from the probe prior to advancing the array electrodesthrough the probe.
 84. A method as in claim 81, wherein advancing thearray electrodes comprises advancing them forwardly from a distal end ofthe probe so that the electrodes evert outwardly as they are advancedinto the tissue.
 85. A method as in claim 81, wherein the arrayelectrodes deploy outwardly to a radius from 0.5 cm to 3 cm whereinfully distally extended.
 86. A method as in claim 79 or 80, wherein thefirst array electrodes are deployed at a depth below the tissue surfacein the range from 2 cm to 10 cm.
 87. A method as in claim 81, furthercomprising removably attaching an second electrode to the probe afterthe array electrodes have been advanced.
 88. A method as in claim 79,wherein the high frequency current is applied first through the firstarray of electrodes to necrose tissue at or near a boundary of thetarget region to inhibit blood flow into the target region.
 89. A methodas in claim 79 or 80, wherein the cover comprises a rigid plate.
 90. Amethod as in claim 79 or 80, wherein the cover comprises a conformablesurface.
 91. A method as in claim 79 or 80, wherein the cover iscomposed of an electrically non-conductive material.
 92. A method as inclaim 79 or 80, wherein the cover and first electrode array are drawntogether with a force of at least 0.5 psi.